1. Field of the Invention
The present invention relates to an nB2P coding/decoding device with a line code function for easily transmitting data and recoverring data from a transmission line, and a channel code function for detecting errors in the retrieved data.
2. Discussion of Related Art
In general, a line code and a channel code are used individually in data transmission or data link.
The line code used for high speed transmission requires many transitions, a good direct current balance, and a small increase in the transmission line bit speed compared to the source bit speed. For example, a scrambled NRZ (None Return to Zero), a code mark inversion (CMI), and 8B10B code (U.S. Pat. No. 4,486,739 by Peter A. Franaszek, Albert X. Widmer) are widely used line codes.
But, among those conventional line codes, the scrambled NRZ limits the number of the transition , and CMI requires a large increase in the transmission bit speed. In addition, the scrambled NRZ, CMI, and 8B10B should use an additional channel code for detecting line errors. Specifically, the 8B10B code is widely used for data links. Since the transmission bit speed of 8B10B is increased slightly by 10/8 and its DC balance is good, it is used in the computer network. But the 8B10B is a line code, and therefore it needs an additional channel code for detecting errors generated in the line. Also, when the serially transmitted bits are reconstituted into bytes, the 8B10B uses a complex algorithm or restricts the source data for the byte-synchronization, because the signal used for the byte synchronization is not orthogonal.
A method of making a code by adding a widely used parity bit to a data bit is the most suitable for a cyclic code among block codes. The method adds the parity to the data so that the block becomes an even or odd number. This invention is based on a parity code method which is a kind of the block codes described above. The method can detect data errors, because the method pertains to channel codes, but the method cannot ensure the number of transitions in the data bit and the complex method requires byte synchronization detection for the serially transmitted data.